During the past year an effort to determine the feasibility and likelihood of success of a national cooperative study of mycosis fungoides has been in progress. This narrative will outline (1) the problems that we see inherent to a cooperative study of mycosis fungoides, (2) the reasons that such a cooperative study is, nevertheless, imperative, (3) work so far completed and (4) our plan for implementation of such a study. Mycosis fungoides is an uncommon but not rare malignancy of the lympho reticular system accounting for about 1 percent of the lymphoma deaths in the U.S.A. There are perhaps 2,000 to 4,000 new cases per year; with the larger institutions seeing 10 to 30 new cases per year. As the disease may last for many years a fairly large reservoir of total cases, therefore, exists. In addition to the incidence of this condition, there has been interest in mycosis fungoides because of observations charging the delayed hypersensitivity system in the control of this neoplasm. Any cooperative effort, particularly where protocol therapy is concerned, will require standardization of histologic and clinical criteria as a matter of first importance. Although definitive therapy for mycosis fungoides is not yet available, reports on small series of patients and many individual case reports have clarified, at least, the present most useful treatment modalities. A study to determine which is superior has not been done. Yet unresolved is the intriguing matter that most of the therapies presently used interfere with immunologic defenses. Two formal meetings were held in Chicago during the project period for the purpose of examining the application of mycosis fungoides to a national cooperative effort. The first was on September 8-9, 1971; the second was on December 3, 1971. The meetings are summarized in the narrative.